Back strength cannot be predicted accurately from anthropometric measures in subjects with and without chronic low back pain

The Relationship Between Pain-Related Psychological Factors and Maximal Physical Performance in Low Back Pain: A Systematic Review and Meta-Analysis

Theoretical frameworks explain how pain-related psychological factors may influence the physical performance. In this systematic review and meta-analysis, we evaluated the evidence regarding the relationship between the pain-related psychological factors and the maximal physical performance in patients with low back pain (LBP). Pubmed, Embase, CINAHL and Web of Science databases were searched from inception to May 2022. Cross-sectional or longitudinal studies reporting cross-sectional measures of association between at least one pain-related psychological factor and a quantitatively measured outcome of maximal physical performance in patients with LBP were eligible for inclusion. Thirty-eight studies (n = 2,490; 27 cross-sectional studies, n = 1,647 (66%); 11 longitudinal studies, n = 843 (34%)) were included, with 92% of participants (n = 2,284) having chronic LBP. Results showed that pain-related fear, pain catastrophizing, and anticipated pain were consistently and negatively associated with the maximal physical performance in chronic LBP, whereas pain-self efficacy showed positive correlations. Overall, magnitudes of absolute pooled r-values were small (r ≤ 0.25), except for anticipated pain, which was moderately associated with maximal physical performance (r = -0.34 to -0.37). Subanalyses and sensitivity analyses yielded similar pooled correlation coefficients. Certainty of evidence using the GRADE recommendations was very low to moderate for pain-related fear, and very low to low for the other pain-related psychological factors. Prospero registration: CRD42021227486. PERSPECTIVE: Overall, small pooled correlation coefficients were shown between pain-related psychological factors and maximal physical performance in chronic LBP. Certainty of evidence was very low to low for all pain-related psychological factors other than pain-related fear. Future studies taking into account limitations of the current literature may therefore change these conclusions.

Trunk musculoskeletal response in maximum voluntary exertions: A combined measurement-modeling investigation

Maximum voluntary exertion (MVE) tasks quantify trunk strength and maximal muscle electromyography (EMG) activities with both clinical and biomechanical implications. The aims here are to evaluate the performance of an existing trunk musculoskeletal model, estimate maximum muscle stresses and spinal forces, and explore likely differences between males and females in maximum voluntary exertions. We, therefore, measured trunk strength and EMG activities of 19 healthy right-handed subjects (9 females and 10 males) in flexion, extension, lateral and axial directions. MVEs for all subjects were then simulated in a subject-specific trunk musculoskeletal model, and estimated muscle activities were compared with EMGs. Analysis of variance was used to compare measured moments and estimated spinal loads at the L5-S1 level between females and males. MVE moments in both sexes were greatest in extension (means of 236 Nm in males and 190 Nm in females) and least in left axial torque (97 Nm in males and 64 Nm in females). Being much greater in lateral and axial MVEs, coupled moments reached ∼50% of primary moments in average. Females exerted less moments in all directions reaching significance except in flexion. Muscle activity estimations were strongly correlated with measurements in flexion and extension (Pearson's r = 0.69 and 0.76), but the correlations were very weak in lateral and axial MVEs (Pearson's r = 0.27 and 0.13). Maximum muscle stress was in average 0.80 ± 0.42 MPa but varied among muscles from 0.40 ± 0.22  MPa in rectus abdominis to 0.99 ± 0.29 MPa in external oblique. To estimate maximum muscle stresses and evaluate validity of a musculoskeletal model, MVEs in all directions with all coupled moments should be considered.

Decline in lumbar extensor muscle strength the older adults: correlation with age, gender and spine morphology

BACKGROUND

Muscle morphology, age and gender may be determinants of muscle strength in older adults. However, very few research studies have directly examined such correlation in the ageing spine. The aim of the study was to examine the correlation between lumbar extensor muscle strength, its muscle fibre angles, thoracolumbar curvature, age and gender in the older and younger adults.

METHODS

Muscle fibre angles of lumbar extensor muscles, thoracolumbar curvature and lumbar extensor muscle strength were examined in 26 young (mean age 27.9, SD 5.2) and 26 older (mean age 72.1, SD 5.9) participants. Pearson's correlation was employed to determine the association among lumbar extensor muscle fibre angle, thoracolumbar curvature, age, gender and lumbar extensor muscle strength. Multiple stepwise linear regression analysis was used to identify significant determinants of lumbar extensor muscle strength.

RESULTS

The results demonstrated a significant correlation between lumbar extensor muscle strength, muscle fibre angle, age and gender. In the step wise regression analysis, both gender and age were identified as the most robust determinant for lumbar extensor muscle strength in older adults. However, gender was the only determinant of muscle strength in the young.

CONCLUSION

These results suggest that the decline in the lumbar extensor muscle strength in older adults was more dependent on age when compared to younger adults.

The association of nutritional status and gender with cross-sectional area of the multifidus muscle in establishing normative data

Despite recognized evidence for the importance of the multifidus muscle in stabilizing the lumbar spine, identifying subjects at risk for injury and subsequent loss of intrinsic spinal stabilization remains difficult. Previous research has failed to associate multifidus muscle size and height, weight, or body mass index (BMI). The purpose of this study was to begin to establish normative data for the multifidus muscle cross-sectional area (CSA) at the L5 level and to identify factors associated with size. Twenty-five participants (17 female), with a mean age of 32.5 (SD 11.6) years without history of LBP were considered for inclusion. Participants' height and weight were recorded and BMI calculated. Ultrasound imaging was used to obtain a CSA in cm(2) of the subjects' multifidus muscles at the L5 level bilaterally; testing was done by two trained testers. Prior to testing, intra- and inter-tester reliability were determined. Percent body fat was determined using a three-site skinfold caliper measurement, also using two trained testers. Mean BMI was 24.18 and mean body fat (%) was 22.88 for all participants. As expected, age and BMI were moderately correlated. Left and right multifidus muscle CSA were highly correlated (r = 0.92, p < 0.001). The mixed model ANOVA indicated a significant main effect for gender as males exhibited larger CSA than females. Participants without history of low back pain present with symmetrical multifidus muscle CSA at the L5 level. Clear gender differences in CSA show that males tend to have larger multifidus muscles at the L5 level, indicating a need to establish gender-specific norms for clinicians examining the L5 multifidus muscle.

Poor back muscle endurance is related to pain catastrophizing in patients with chronic low back pain

STUDY DESIGN

An experimental and comparative study of chronic low back pain (CLBP) patients and healthy controls.

OBJECTIVE

To use a motivation-independent electromyography (EMG) based test of back muscle capacity to determine whether back muscle deconditioning is present in CLBP patients and whether it is related to pain-related psychological variables.

SUMMARY OF BACKGROUND DATA

The verification of the deconditioning syndrome in CLBP patients might be biased by the use of performance-based measures to assess physical fitness, especially in patients having fear of injury. Also, the use of lumbar-specific measures of physical fitness, such as back muscle strength and endurance, might be more sensitive to physical deconditioning than more general assessments such as aerobic capacity.

METHODS

A time-limited submaximal fatigue test was performed by 27 nonspecific CLBP subjects (14 men) who had not had any surgery, and 31 healthy controls (17 men) while surface EMG signals were collected from back muscles. Motivation-independent EMG indices, which are sensitive to muscle fatigue or to activation patterns, were then computed and entered as input into previously developed regression equations to predict endurance (PTend) and strength (PStrength). Between-group comparisons were completed with patients divided in subgroups based on a median split of pain intensity, fear of movement, or pain catastrophizing scores.

RESULTS

Differences between healthy and CLBP subgroups were mainly observed when patients were divided using pain catastrophizing scores (PCS). High-PCS patients showed significantly lower PTend than low-PCS patients. Various EMG indices showed comparable results to PTend. However, some of them also pointed out that the PCS-low patients were more fatigue-resistant and showed different activation patterns comparatively to healthy subjects.

CONCLUSION

These results suggest that physical deconditioning that is specific to back muscle capacity was present in a subgroup of patients while the opposite was observed in another subgroup, pain catastrophizing being related to this outcome. These findings support previous theoretical models of pain/disability.

Toward the development of predictive equations of back muscle capacity based on frequency- and temporal-domain electromyographic indices computed from intermittent static contractions

BACKGROUND CONTEXT

Back muscles capacity is impaired in chronic low back pain patients but no motivation-free test exists to measure it. A functional endurance test (FET) was used to assess capacity of back muscles using surface electromyographic (EMG) indices as outcome measures.

PURPOSE

The main objective of the present study was to explore the possibility of combining different types of EMG indices to predict absolute endurance and strength.

STUDY DESIGN/SETTING

A cross-sectional study using a repeated measures design in laboratory setting.

METHODS

Healthy subjects (44 men and 29 women) performed maximal voluntary contractions (Strength criterion: extension moment at L5/S1) and a fatigue test involving intermittent static extension contractions to exhaustion (Tend endurance criterion: time to reach exhaustion). Surface EMG signals were collected from four pairs of back muscles. From the first 5 minutes (women) or 10 minutes (men) of EMG data, frequency- and temporal-domain analyses were applied to compute various EMG indices.

RESULTS

Strength values ranged from 153 to 508Nm, whereas Tend values ranged from 3 to 57 minutes across the subjects. Gender-specific multiple regression equations were developed, using the retained EMG indices from the four electrode sites, to predict Tend (men: R(2)=0.76, error=9%; women: R(2)=0.70, error=17%) and Strength (men: R(2)=0.72, error=9%; women: R(2)=0.25, error=13%).

CONCLUSIONS

It appears to be possible to predict the capacity of back muscles using an intermittent and time-limited (submaximal) fatigue task. Frequency- and temporal-domain EMG indices were shown to provide complementary information in this respect. This FET has potential to better infer back muscle capacity for realistic occupational tasks because more specific muscle fatigue mechanisms are involved.

The assessment of back muscle capacity using intermittent static contractions. Part I – Validity and reliability of electromyographic indices of fatigue

INTRODUCTION

Back muscle capacity is impaired in chronic low back pain patients but no motivation-free test exists to measure it. The aims of this study were to assess the reliability and criterion validity of electromyographic indices of muscle fatigue during an intermittent absolute endurance test.

METHODS

Healthy subjects (44 males and 29 females; age: 20-55 yrs) performed three maximal voluntary contractions (MVC) and a fatigue test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The fatigue test, assessing absolute endurance (90-Nm torque), consisted in performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the fatigue test. From the first five min (females) or ten min (males) of EMG data, frequency and time-frequency domain analyses were applied to compute various spectral indices of muscle fatigue.

RESULTS

The EMG indices were more reliable when computed from the time-frequency domain than when computed from the frequency domain, but showed comparable correlation results (criterion validity) with Tend and Strength. Some EMG indices reached moderate to good correlation (range: 0.64-0.69) with Tend, lower correlations (range: 0.39-0.55) with Strength, and good to excellent between-day test-retest reliability results (intra-class correlation range: 0.75-0.83). The quantification of the spectral content more locally in different frequency bands of the power spectrum was less valid and reliable than the indices computed from the entire power spectrum. Differences observed among muscles were interpreted in light of specific neuromuscular activation levels that were observed during the endurance test. These findings supported the use of an intermittent and time-limited (5-10min) absolute endurance test, that is a practical way to assess the back capacity of chronic low back pain subjects, to assess absolute endurance as well as strength with the use of electromyographic indices of muscle fatigue.

Prediction of back strength using anthropometric and strength measurements in healthy females

OBJECTIVES

The purpose of this study was to develop a regression equation to predict back extensor maximal voluntary contraction (back strength) for females based on several anthropometric and strength measurements using a multiple regression technique.

BACKGROUND

Back strength is an important parameter in low back pain studies. However, the measurement of back strength is problematic in certain populations such as low back pain patients and pregnant women.

METHODS

Back strength was measured as both moment at L4/L5 and force. Ten anthropometric or strength measurements were chosen to develop the prediction equation. The data used for developing the models were from eighty non-pregnant female subjects, age 18-42 and with no history of back pain in the past year. Backwards stepwise analysis was performed in order to choose the best fit predictors. The predictive ability of each of the models was checked using the cross-validation technique on 20 other subjects.

FINDINGS

Two prediction models were developed for moment and force, respectively. The models explained 46.9% and 48.2% of the variance in back strength. No multicollinearity problem was found. The validation study showed that the observed back strength was highly correlated with the predicted back strength.

INTERPRETATION

Mass, height, trunk length, grip strength and quadriceps strength are the best predictors of back strength in this study. The models developed in this study can be used for both general female low back pain patients and the pregnancy population.

Surface electromyography assessment of back muscle intrinsic properties

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.